1. Field of the Invention
The present invention relates to a data conversion circuit and a color image display apparatus for displaying a square arrangement image in a non-square cell arrangement screen, which is particularly suitable for a display using a plasma display panel (PDP).
2. Description of the Prior Art
Recently, high image quality of a television set or a computer output is widely spread, and a display apparatus is desired that supports a high definition display for various kinds of images including a natural image or a character image.
As a display device having a large screen, a surface discharge format AC type PDP is put into commercial production. The surface discharge format is a format in which first and second display electrodes to be anodes and cathodes in display discharge for securing luminance are arranged in parallel on a front or a back substrate. As an electrode matrix structure for the surface discharge type PDP, a “three-electrode structure” is common in which address electrodes are arranged so as to cross the display electrode pairs. For a display, one of the display electrode pair is used as a scan electrode for row selection in a matrix display, and address discharge is generated between the scan electrode and the address electrode so that addressing is performed for controlling wall charge in accordance with display contents. Hereinafter, a pixel array in the row direction of an image as well as a cell array in the row direction of a display screen is called a “line”. In addition, a line of the display screen is called a “display line” if discrimination is necessary.
In Japanese unexamined patent publication No. 9-50768, a deformed stripe partition structure is proposed in which the three-electrode surface discharge type PDP has plural band-like partitions that divide a discharge space in the direction along the display line (usually in the horizontal direction) and meander in a regular manner so as to prevent discharge interference in the direction along the column (usually in the vertical direction). Each of the partitions defines a column space with a neighboring partition. The column space has wide portions and narrow portions that are arranged alternately. Positions of the wide portions in the neighboring columns are shifted from each other, and a cell is formed in each of the wide portions. One of red, green and blue fluorescent materials is arranged in each column space for a color display so that light emission color is different between neighboring column spaces. The three colors are arranged in a so-called delta arrangement (a delta tricolor arrangement). Since the delta arrangement has a cell width larger than one third of a pixel pitch in the display line direction and an aperture ratio larger than a square arrangement, a display with higher luminance can be achieved. Conventionally, in a color image display using a delta arrangement PDP, each of the display lines is made up of cells each of which is selected fixedly from the cell array along each address electrode.
In a display apparatus having a usual square cell arrangement display device, resolution conversion is performed for adjusting an image size to a display device so as to display various sizes of input images. The size conversion in the horizontal direction is performed by adjusting timing of a sampling clock when converting an analog image signal into digital image data. The size conversion in the vertical direction is performed by interpolation operation on the basis of data of plural lines. For example, data of a new line that are generated from a mean value of data of two neighboring lines are inserted between the original two lines, so that the number of lines can be doubled. In addition, the number of lines can be reduced in half by outputting the generated data of the line instead of the original two lines.
Conventionally, there was a problem that an unnatural display is produced because of the following two phenomena when adopting a delta arrangement display screen.
(1) Since positions of neighboring cells are shifted from each other in the vertical direction, a line extending in the horizontal direction looks like a zigzag line in the display.
(2) Pitches of lighted cells are not uniform when displaying a line slanting to the horizontal direction and the vertical direction.